Discipline: Biological Sciences
Mariby Cruz - California State University, Chico
Co-Author(s): Co-Authors: Diana Lieberman & Milton Lieberman, Undergraduate Research Opportunities Center, California State University, Monterey Bay
ABSTRACT. Many species of trees growing in non-seasonal tropical environments do not form reliable annual growth rings. Determination of tree age and projection of lifetime growth curves cannot therefore be done directly by tree ring analysis. Data on tropical tree growth is applicable to the fields of tropical forest ecology and management, conservation of biodiversity, and climate change.
An analytical modeling technique, Growth Simulation, has been applied in published analyses of tropical tree growth. Growth Simulation uses randomly sampled diameter increments of tagged trees over a known time interval to assemble model lifetime growth trajectories. The simulation yields the maximum, median, and minimum growth rates; maximum longevity; and the minimum number of years necessary to reach the maximum size.
Here we report the first independent validation of Growth Simulation using pine trees for which annual growth rings can be readily counted and measured. We test the hypothesis that the model outputs of Growth Simulation conform to the actual growth curves derived from tree ring analysis in these trees.
The growth history of 55 pine branches was documented by counting and measuring each growth ring to the nearest 0.1 cm. Branches ranged in age from 8 to 35 years. For a given test branch, the annual diameter increments over the life of the branch were entered as the input for Growth Simulation, and the model output compared with the test branch. Median diameter growth rate and estimated longevity from the model closely matched values for the individual test branch and reflected year-to-year variability in growth rates within the branch. Diameter increments over 5-yr intervals, sampled at random starting points on each test branch, were then used as input data, and the results compared with the test branches. Statistical analysis showed close correspondence between the model estimates and the branch data in terms of maximum, median, and minimum growth rates and estimated branch longevity. Results strongly support the utility and rigor of Growth Simulation modeling in studies of tropical trees for which growth ring analysis is not feasible. Potential applications of Growth Simulation lie in any area where periodic increments are available for long-lived organisms; examples would include corals, fish, sea turtles, or crocodiles.
References: Lieberman, D., and M. Lieberman. 1985. Simulation of growth curves from periodic increment data. Ecology 66:632-635.
Funder Acknowledgement(s): Funding for the research provided through NSF grant HRD 0802628 to California State University-LSAMP and the Chancellor's Office, California State University
Faculty Advisor: Drs. Diana and Milton Lieberman, firstname.lastname@example.org
Role: For the validation of Growth Simulation, my contribution dealt with the collection of raw data. This meant that I made decisions on how and what to measure on the seasonal tree branches. With the help of my mentors, we worked together to develop the question and to decide upon the best analytical approaches. With this I imported the data into GW-Basic and applied the Growth Simulation, a simulation already used in tropical research. Together, we interpreted the results from the simulation. We are also in the process of writing a paper to be submitted to a peer-reviewed journal.